Study on the Time-Frequency Domain Response Characteristics of Narrowband Antennas to Ultra-Wideband Electromagnetic Pulses

This paper investigates the time-frequency domain response characteristics and coupling mechanisms of ultra-wideband electromagnetic pulses (UWB-EMP) on narrowband antennas. Through numerical simulations, we elucidate how the relationship between an antenna's resonant frequency f0 and the incident pulse's spectrum (fL-fH) governs the resultant response waveform. The evolution of the response waveform is systematically characterized: For an in-band antenna (fL<f0<fH), impedance matching leads to a coupled signal whose spectral energy is predominantly confined within the antenna's passband, resulting in a damped oscillatory timedomain waveform. For an above-band antenna (fH<f0), the antenna behaves capacitively, coupling a broad spectral signal. The time-domain waveform approximates the first derivative of the incident field, exhibiting a faster rise time and narrower pulse width. This differential effect becomes more pronounced when the antenna's maximum dimension D is electrically small (D<λH / 10), where λH is the shortest wavelength of the incident pulse). For an Below-band antenna (f0<fL), When the incident pulse width is shorter than the transit time τ of the coupled signal along the antenna, the response manifests as multipulse waveform, with the pulse interval determined by the antenna's structural dimensions. These findings are crucial for understanding the time-frequency domain response of UWBEMP and for analyzing their effect mechanisms on electronic systems.